Design and Fabrication of a Rectangular He-Cooled Refractory Foam HX-Channel for Divertor Applications

A rectangular single channel low pressure drop helium-cooled refractory metal heat exchanger (HX) tube for divertor applications was designed and manufactured for testing in the SNL E-beam facility. A unique fabrication feature of the rectangular HX channel design is that all welds, brazes, and joints are located at or near the bottom of the rectangular channel, i.e., far from any heated surface. The HX tube concept uses a thin (~2mm) layer of open-cell refractory foam bonded underneath the heated surface to enhance heat transfer to the helium coolant.

The helium coolant flows through a 2-mm-wide slot and then through the thin foam layer (~2 mm × 12 mm × 127 mm; H/W/L) from the inlet to the outlet plenum. This design minimizes the path of helium flow through foam to about 11 mm and thus the pressure drop through the porous media is more or less constant along the length of the channel. The concept is scalable for cooling large flat surfaces, such as a flat-plate divertor, without substantially increasing the coolant pressure losses.

We present CFD analyses used to optimize the design for minimum pressure drop through the porous media and for highest uniformity of surface temperatures. A design-for-manufacturing concept for a single HX-channel was developed with the goal to minimize welds or joints near heated surfaces. Based on the advanced HX-channel design a number of HX-channels were manufactured using Mo as a surrogate material instead of tungsten.